1. Field of the Invention
The invention relates to a unit that detects a condition related to the operating life of a spindle of a machine tool.
2. Discussion of Background
For example, Japanese Patent Application Publication No. 11-28644 describes a method for managing maintenance of a spindle of a machine tool. According to Japanese Patent Application Publication No. 11-28644, a load on a spindle is detected by using a current sensor or a torque sensor provided at a spindle motor, the operating time of the spindle is accumulated for each level of load, and then each of the accumulated operating times is converted into operating time at a reference load level. Then, a relevant part is replaced if the total operating time obtained by adding up the operating times obtained through conversion has reached a reference value. According to this technique, operators are able to realize that, for example, a spindle taper portion of the spindle has reached the end of its operating life, allowing proper maintenance of the spindle taper portion.
According to the technique described in Japanese Patent Application Publication No. 11-28644, the operators are able to realize that the spindle has reached the end of its operating life. However, the inventors have found it important to ascertain, for example, the remaining operating life of the spindle at the present moment. In particular, ascertaining a present condition related to the operating life of the spindle may contribute to an increase in the machining efficiency. In addition, the inventors have found it most important to ascertain the operating life of a bearing that rotatably supports a spindle of a machine tool, and thus considered that it is necessary to ascertain a condition related to the operating life of the bearing for the spindle at the present moment.